The present invention relates generally to a method of designing a physical layout of a semiconductor integrated circuit, and, more particularly, to a metallization stack to be located on a major surface of a semiconductor substrate of an integrated circuit.
Integrated circuits generally include a semiconductor substrate including active or passive components (transistors, diodes, etc.), and a metallization stack provided on a major surface of the substrate. The metallization stack includes a plurality of patterned metal layers separated by intervening dielectric. The metal layers in the stack can be used to route, for instance, power supply lines, ground lines and signal lines within the integrated circuit.
Electromagnetic attacks against secure integrated circuits involve placing an induction loop over a surface of the integrated circuit to attempt to detect currents passing within the metal levels of the metallization stack.
When designing integrated circuits, it is often required to apply changes to the design at a relatively late stage in the design and manufacturing process. State of the art integrated circuits may contain measures to apply post mask changes to the design without recreation of the complete mask set. Where possible, the design changes may be limited to the backend layers to save both time and cost. Wafers may be stopped after manufacturing of the frontend layers and stored for later completion. The changes may be applied by adding, removing or changing connections between cells of the integrated circuit. Furthermore, spare cells or spare filler cells may be included to provide more flexibility in changing or correcting the functionality of the design.
The implementation of the changed connectivity may involve re-routing in the backend layers, including vias and metal lines thereof, to remove, change or add connections between existing cells or to include the spare cells in these connections. The implementation of the new connectivity typically requires changes in the backend stack of metal and via layers, which in turn requires changes to at least some of the metal layer and via layer masks used to manufacture the stack. Making changes to one or more masks of the mask set may lead to shipping delays and may be expensive.